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Every generation of each and every species resembles its ancestors in many ways. How are these characteristics transmitted from one generation to the next? It has been observed that nucleus of a living cell is responsible for this transmission of inherent characters, also called heredity. The particles in nucleus of the cell, responsible for heredity, are called chromosomes which are made up of proteins and another type of bimolecular called nucleic acids. These are mainly of two types, thedeoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Since nucleic acids are long chain polymers of nucleotides, so they are also called polynucleotides. Why is a dog a dog and not a cat? Why do some people have blue or brown eyes and not black? From a chemical standpoint, how does the body know what particular type of protein is to be synthesized? How is this information transmitted from one generation to the next? The study of the chemistry of heredity is one of the most fascinating fields of research today. It was recognized in the 19th century that the nucleus of a living cell contains particles responsible for heredity, which were called chromosomes. In more recent years, it has been discovered that chromosomes are composed of nucleic acids. These are named so because they come from the nucleus of the cell and are acidic in nature. Two types of nucleic acids exist which are called DNA and RNA. They differ in their chemical composition as well as in functions. Like amino acids which are the building blocks of proteins, nucleotides are the building blocks of the nucleic acids, RNA and DNA. Aside from these major biological roles, nucleotides are important players in energy metabolism, coenzymes, and intermediary metabolism. Nucleotides are composed of a nitrogenous base, a sugar, and a phosphoryl group. Removal of phosphoryl group results in a compound known as a nucleoside. There are two types of bases found in nucleotides, purines and pyrimidines. The sugars are either D-ribose or 2-deoxy-D-ribose.
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